Implement HMAC support in lib/crypto.

lib/crypto/crypto.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #library('crypto');
 
+#source('hmac.dart');
 #source('sha_utils.dart');
 #source('sha1.dart');
 #source('sha256.dart');
 
 /**
  * Interface for cryptographic hash functions.
  *
  * The [update] method is used to add data to the hash. The [digest] method
- * is used to extract the message digest. Once the [digest] method has been
- * called the CryptoHash object is in an invalid state and should not be
- * used again. If [digest] or [update] are called after the first call to
- * [digest] a CryptoHashException is thrown.
+ * is used to extract the message digest.
+ *
+ * Once the [digest] method has been called no more data can be added using the
+ * [update] method. If [update] is called after the first call to [digest] a
+ * HashException is thrown.
+ *
+ * If multiple instances of a given Hash is needed the [newInstance]
+ * method can provide a new instance.
  */
-interface CryptoHash {
+interface Hash {
   /**
    * Add a list of bytes to the hash computation.
    */
-  CryptoHash update(List<int> data);
+  Hash update(List<int> data);
 
   /**
    * Finish the hash computation and extract the message digest as
    * a list of bytes.
    */
   List<int> digest();
+
+  /**
+   * Returns a new instance of this hash function.
+   */
+  Hash newInstance();
+
+  /**
+   * Block size of the hash in bytes.
+   */
+  int get blockSize();
 }
 
 /**
  * SHA1 hash function implementation.
  */
-interface SHA1 extends CryptoHash default _SHA1 {
+interface SHA1 extends Hash default _SHA1 {
   SHA1();
 }
 
 /**
  * SHA256 hash function implementation.
  */
-interface SHA256 extends CryptoHash default _SHA256 {
+interface SHA256 extends Hash default _SHA256 {
   SHA256();
 }
 
 
 /**
- * CryptoHashExceptions are thrown on invalid use of a CryptoHash
+ * Hash-based Message Authentication Code support.
+ *
+ * The [update] method is used to add data to the message. The [digest] method
+ * is used to extract the message authentication code.
+ */
+interface HMAC default _HMAC {
+  /**
+   * Create an [HMAC] object from a [Hash] and a key.
+   */
+  HMAC(Hash hash, List<int> key);
+
+  /**
+   * Add a list of bytes to the message.
+   */
+  HMAC update(List<int> data);
+
+  /**
+   * Perform the actual computation and extract the message digest
+   * as a list of bytes.
+   */
+  List<int> digest();
+}
+
+
+/**
+ * HashExceptions are thrown on invalid use of a Hash
  * object.
  */
-class CryptoHashException {
-  CryptoHashException(String this.message);
-  toString() => "CryptoHashException: $message";
+class HashException {
+  HashException(String this.message);
+  toString() => "HashException: $message";
   String message;
 }